Artifactually elevated serum bicarbonate results caused by elevated serum lactate dehydrogenase concentrations

Abstract

An accurate estimation of serum bicarbonate concentration (HCO3(-)) is essential to the diagnosis and treatment of acid-base disorders and electrolyte disturbances. We noted significant discrepancies between HCO3(-) concentration measured by the Olympus AU2700 analyser and total serum carbon dioxide (TCO2) concentration derived from a Radiometer blood gas analyser on several patient samples. This was reported to the manufacturer which led to a recall of certain reagent lot numbers. We hypothesised the mechanism for this interference to be elevated levels of lactate dehyrogenase (LD). We investigated the effect of increasing LD concentration on HCO3(-) with the reagent lot that was recalled and compared this with a subsequent reagent lot that was known to be unaffected on an Olympus AU2700. The experimental data confirmed a positive interference in the Olympus AU2700 HCO3(-) assay using older reagent lot numbers. The false positive HCO3(-) interference was significant (>10% change) when the LD concentration exceeded 845 U/L. Very high levels of LD concentrations were the cause of interference in the Olympus AU2700 HCO3(-) enzymatic assay. Laboratorians should be aware that very high levels of LD may be a potential interference in some enzymatic HCO3(-) assays.